A fast burning engine is known to have low cyclic variation in cylinder pressure as well as greater resistance to engine knock. This leads to higher engine efficiency through higher compression ratio.
One way to achieve fast burning is torch jet ignition. A typical torch jet igniter comprises a large prechamber coupled to a main combustion chamber through a large orifice, usually greater than 5 mm, and a spark plug in the prechamber. The volume of the prechamber is 3 to 12% of the clearance volume. Since ignition occurs in the prechamber, the mixture in the prechamber is very critical; therefore, a valve in the prechamber is normally required to provide a fresh mixture to the prechamber. After ignition, the burned mixture in the prechamber will expand into the main combustion chamber through the orifice and form a torch jet. The enhanced burning rate comes from the higher turbulence induced by the jet and from the larger flame front area created by the torch jet at its boundary. In some cases special valving has been avoided.
An example of a torch jet ignition system without special valving is shown in U.S. Pat. No. 3,921,605 to Wyczalek which proposes a large prechamber having a volume of 2 to 10% of the total clearance volume, a range of 5 to 15 cubic inches of volume for each square inch of orifice area, an orifice size of about 3.6 mm in diameter, and a special spark plug within the chamber. On the other hand, U.S. Pat. No. 4,112,877 to Goto et al discloses a prechamber with special valve arrangements for introducing a fresh air-fuel mixture into the chamber. The spark plug is remote from the prechamber. Another example of prechamber devices is in U.S. Pat. No. 4,096,844 to Mackaness which shows various styles including a prechamber remote from the spark plug and a prechamber containing a spark plug. The prechambers appear to be quite large but no dimensions are given.
The disadvantages of providing for the large prechamber and for providing any special valving are evident. It is also apparent that with this arrangement, an engine must be specially designed to take advantage of the torch jet ignition. The present invention proposes a new way to achieve fast burning using a torch jet which requires a very small torch chamber (smaller than 1% of the volume of the main combustion chamber) and can even fit within a spark plug for use in any engine. Moreover, no valving is needed.
Small chambers associated with ignition and even chambers incorporated in spark plugs are already known. For example, U.S. Pat No. 4,639,635 to Lee discloses an extremely small chamber (28 mm 3 volume) having two spark gaps, one within the chamber to effect heating and discharge of the gas from the chamber and another in the gas discharge path to ionize the gas thereby producing a low energy plasma jet.